1. Field of Inventions
The present inventions relate generally to devices for performing operations on body tissue.
2. Description of the Related Art
Clamps are used in a wide variety of medical procedures. For example, clamps that carry electrodes or other energy transmission elements on opposable clamp members are used in a number of electrophysiology procedures, especially those in which the physician intends to position electrodes on opposite sides of a body structure to form a therapeutic lesion. Therapeutic lesions are frequently formed to treat conditions in the heart, prostate, liver, brain, gall bladder, uterus, breasts, lungs and other solid organs. Electromagnetic radio frequency (“RF”) may, for example, be used to heat and eventually kill (i.e. “ablate”) tissue to form a lesion. During the ablation of soft tissue (i.e. tissue other than blood, bone and connective tissue), tissue coagulation occurs and it is the coagulation that kills the tissue. Thus, references to the ablation of soft tissue are necessarily references to soft tissue coagulation. “Tissue coagulation” is the process of cross-linking proteins in tissue to cause the tissue to jell. In soft tissue, it is the fluid within the tissue cell membranes that jells to kill the cells, thereby killing the tissue. The tissue coagulation energy is typically supplied and controlled by an electrosurgical unit (“ESU”) during the therapeutic procedure. More specifically, after an electrophysiology device has been connected to the ESU, and the electrodes or other energy transmission elements on the device have been positioned adjacent to the target tissue, energy from the ESU is transmitted through the energy transmission elements to the tissue to from a lesion. The amount of power required to coagulate tissue ranges from 5 to 150 W.
Examples of clamp based devices which carry energy transmission elements are disclosed in U.S. Pat. No. 6,142,994, and U.S. Patent Pub. No. 2003/0158547 A1, which are incorporated herein by reference. In a typical clamp based procedure, a clamp will be used by the physician to position energy transmission elements on opposite sides of a tissue structure. Energy may then be transmitted through the tissue from one energy transmission element to the other, which is commonly referred to as bipolar energy transmission, or from each of the energy transmission elements to an indifferent electrode positioned at a remote location such as the patient's skin, which is commonly referred to as unipolar energy transmission.
Some clamps are designed such that the clamp members remain parallel to one another (or at least approximately parallel to one another) as the clamp moves from a closed orientation to an open orientation and back. Maintaining the parallel relationship serves a number of important purposes. For example, it may be important that the electrodes on the clamp members be parallel to one another when the tissue structure is engaged, regardless of the thickness of the tissue structure. The parallel relationship also reduces the maximum distance that the distal most portions of the clamp members will be from one another when the clamp is being positioned around a tissue structure, as compared to clamps with clamp members that are not configured to maintain a parallel relationship. One conventional method of insuring that the clamp members maintain a parallel relationship is to orient the clamp members such that they are both parallel to the axis about which they are pivoting. In those instances where the clamp includes a pair of arms that are pivotably connected to one another by a pivot pin, the parallel relationship has been heretofore accomplished by orienting the clamp members at 90 degrees to the arms at a location that is significantly distal of the pivot pin. Such clamps have an overall “L” shape.
The present inventors have determined that conventional clamps which maintain the clamp members in a parallel relationship are susceptible to improvement. For example, the present inventors have determined that it is very difficult to insert an L-shaped device through a small port (such as a trocar) during minimally invasive surgical procedures. The present inventors have also determined that the configuration of conventional clamps which maintain the clamp members in a parallel relationship results in a profile, when open, that can be too large for minimally invasive procedures. The present inventors have further determined that the configuration of conventional clamps which maintain the clamp members in a parallel relationship can result in the rotational misalignment of the clamp members when the clamp members are positioned around a tissue structure, which can result in poor electrode-tissue contact in electrophysiological applications.